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    <title>Document</title>
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    <script>
      document.write("求1+2!+3!+...+20!的值");
      document.write("<br>");
      var sum = 0;
      var tmp = 1;
      for (var i = 1; i <= 20; ++i) {
        tmp *= i;
        //tmp为当前数字i的阶乘的值
        sum += tmp;
        document.write(tmp);
        document.write("<br>");
      }
      document.write(sum);
    </script>
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